1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing stimulable phosphor sheets to a radiation passing through an object to have a radiation image of the object stored therein, exposing the stimulable phosphor sheet to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, or cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
In order to reuse stimulable phosphor sheets of the type described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored therein should be erased by exposure to light or heat as described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Patent Application No. 58(1983)-66730 a built-in type radiation image recording and read-out apparatus comprising:
(i) a circulating and conveying means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(ii) an image recording section positioned on said circulation path for recording a radiation transmission image of an object on said stimulable phosphor sheet by exposing said stimulable phosphor sheet to a radiation passing through said object,
(iii) an image read-out section positioned on said circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored therein in said image recording section, and a photoelectric read-out means for detecting light emitted from said stimulable phosphor sheet scanned with said stimulating rays to obtain an electric image signal, and
(iv) an erasing section for, prior to the next image recording on said stimulable phosphor sheet for which the image read-out has been conducted in said image read-out section, having said stimulable phosphor sheet release the radiation energy remaining in said stimulable phosphor sheet, whereby said stimulable phosphor sheet is circulated through said image recording section, said image read-out section and said erasing section and reused for radiation image recording.
Since the radiation image recording and read-out apparatus constructed as described above can continuously and efficiently conduct radiation image recording and read-out, it is suitable for mass medical examinations and for loading on a mobile X-ray diagnostic station in the form of a vehicle like a bus for the purposes of mass medical examinations or the like.
In the aforesaid radiation image recording and readout apparatus, the erasing section is fabricated for exposing the stimulable phosphor sheet to erasing light or heat. When erasing light is used, in order to make the stimulable phosphor sheet practically reusable for image recording, the stimulable phosphor sheet must be exposed to a large light amount (illuminance.times.time), for example, to 10,000 1.times. for 100 seconds. In order to shorten the image erasing time, an erasing light source having as high an output (high illuminance) as possible should be installed at the erasing section. However, in this case, the apparatus becomes large, a power source of a high capacity is necessary, and the large amount of heat generated by the erasing light source has an adverse effect on the other sections of the apparatus. Therefore, the level of the output of the erasing light source has to be limited. Thus in the aforesaid radiation image recording and read-out apparatus, even though the image recording and image read-out processing speeds are increased, the processing speed of the overall apparatus cannot be increased substantially, because a long time is required for image erasing at the erasing section.